Unidirectional radio receiving system



Aug. 14, 1923. l 1,465,108

E. F. W. ALEXANDERSON UNIDIRECTIONAL RADIO RECEIVING SYSTEM Filed Sept.16. 1918 2 Sheets-Sheet 1 Fi l. 9 y 2 32K Ann MMM-.W

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Inventor: Ernst F. W. Alexanderson,

lug. 14, 1923. 1,465,108

E. F. w. ALExANDERsoN UNIDIRECTIONAL RADIO RECEIVING SYSTEM 4 Fig. 7. 46l 42 VWM/44 j fm1 Ei Inventor: Ernst F. W. flexemclerson,

etant ng. 14, i923.

ERNST F. W. .AL

ELECTRIC COMPANY; A CORPORATION OF NEW YORK.

UNIDIRECTIONAL RADIO RECEIVING SYSTEM.

Application tiled September 16, 1918. Serial No. 254,179.

To all whom t may concern.'

Be it known that I, ERNST F. W. ALEX- ANDERsoN, a citizen of the UnitedStates, residing at Schenectady, county of Schenectady, State of NewYork, have invented certain new and useful Improvements inUnidirectional Radio Receiving Systems, of which the following is aspecification.

My present invention relates to radio signaling systems and moreparticularly to a radio receiving system.

One of the objects of my invention is to provide a receiving systemwhich will permit of the reception of signals of any desired wave lengthat a receivin station to the exclusion of other signals aving the sangrewave length ucoming from directions other than that from which thedesired signals come. n l n n Another object of my invention is toprevent interference with the reception of desired signals by aninterfering wave of the same wave length which is produced solely forthe purpose of interference.

Still another object of my invention is to provide a secret radiosignaling system in which it will be impossible for unauthorized personsin some particular locality to receive the signals transmitted from agiven station.. .j

Many dierent forms of .receiving apparatus and antenna may be employedin carrying my invention into efect. In the general embodiment of myinvention two separate fixed receiving antennae may be employed whichare so located with respect to ea other and the direction from whichsignals are to be received that the signaling currents produced in thetwo antennae Aby the desired signals will differ in phase. Thisconditionmay be secured by locating the centers of distribution of the twoantennae at dierent distances from the station from which signals are tobe received. Under these circumstances currents produced by waves comingfrom other directions than that from which the desired signaling wavereaches the antennae except from points located equidistant from thecenters of distribution o f the antennae, will also dili'er in phase;The' phase diderence, however, will be different for waves coming fromdierent directions. In the case of the desired signals, for example, thecurrent in one antenna will lead thatin the y'second antenna while inthe case of signaling waves coming from the opposite direction thecurrent in the second antenna will lead that in the first antenna. Byreason of this difference inthe phase relations of the currents producedin the antennae by waves coming from different directions it is possibleto neutralize in a receiving circuit the currents produced by theundesired waves without neutralizing the el'ect of the currents producedby the desired signaling Waves. In order to secure the desireneutralization it is not necessar that the two sets of waves should comerom opposite directions. While such a condition is preferable, thenecessary phase relations to secure neutralization may exist as lon-g asthe two different stations are located in different directions from thereceiving station.

rlhe currents produced in the two antenn are impressed upon a receivingcircuit. I

introduce between the antennae and the re-` ceiving circuit suitablephase shifting means which are adjusted in such a Way that the currentsproduced by an undesired wave will neutralize each other in thereceiving circuit while the currents produced by the Isignals which itis desired to receive will i act cumulatively in the receiving circuit.

In order to prevent the reception of signals at other points than thereceiving station I produce an interfering wave or waves of the samelength as the signaling wave-at a point or points so located that theinterference in the receiver may be neutralized. If the point or pointswhere it is desired that the signals should not be receivable are alllocated in substantially the same direction from the transmittingstation a single interfering wave set up at some' selected point betweenthe transmitting station and the undesired point-s may 'be suiiicient toproduce the desired result. If, however, there are a large number ofpoints at which it is desired to prevent the reception of signals andthese points are located in somewhat diiferent directions from thetransmitting station it may be desirable to set up two or moreinterfering waves at points so chosen that the interference may beneutralized at the desired receiving station but so located that all ofthe interfering waves can not be neutralized at any one of the undesiredpoints.

My invention will best be understood by reference to the followingdescriptionl taken in connection with the accompanying drawin s inwhich:

ig. 1 shows diagrammatically one form of receiving circuit which may beemployed; Fig. 2 illustrates a convenient form of phase shifter; Fig. 3is a vector diagram illustrating the phase relations of the differentcurrents in the receivin circuit under one condition of operation; igs.4 and 5 show two different forms of receiving diagrams which may beobtained by the use of my invention, and Figs. and 7 show modiiied formsof receiving clrcuits.

I have indicated in Fig. l two transmitting stations A and B from whichsignaling waves of the same length may be transmitted. Between these twostations are located two receiving antennae 1 and 2 extending from thereceiving station 3 toward stations A and B respectively. These antennaeare preferably made up of long horizontal wires stretched a shortdistance above the earth or even lying directly on the ground andinsulated therefrom. In some cases it may be desirable even to have themburied in the earth. For the most eiiicient operation they should pointtoward the two stations. This particular form of antennae as well as thelocation thereof indicated, however, is not essential as will appearfrom the explanation which follows. The only essential feature is thatthe centers of distribution of the two antennae, which in the presentcase are indicated as at the points 4 and 5 should be located atdifferent distances vfrom at least one of stations A and B so that thewaves traveling from both of Y these stations will not strike the tworeceiving antennae simultaneously, and that there will be relatively anappreciable difference 1n time phase of the currents produced by wavestraveling in different directions.

The two antenn are grounded at 6 and the coils 7 and 8 which are inseries with antennae 1 and 2 respectively form the primaries of thevariable intensity coupling transformers 9 and 10 the secondaries 11 and12 .of which are included in two circuits whlch are provided with phaseshifting means. Eachof these circuits should comprise two portionshaving different phase angle characteristics. In the case illustratedthe circuits comprise two branches, one branch which includes resistance13, capacity 14 and inductance 15 and a second parallel branch whichincludes resistance 16 and inductance 17. The two branches arepreferably so designed that the resultant impedance of the lirst branchis capacitative and the resultant impedanceof the second branch isinductive.

Inductances 15 and 17 form the primaries of variable couplingtransformers 18, 19, 20 and 21, thesecondaries 22, 23, 24 and 25 ofwhich are included in a resonant receiving circuit which also' includesan inductance 26 and a tuning condenser 27. Coupling transformers 18 and19 are preferably ariranged to be varied simultaneously so that when thecoupling of one is increased the coupling of thel other is decreased andwhere the coupling of one is a maximum the coupling of the other is aminimum. The manner in which this may be accomplished is shown in Fig. 2in which coils 22 and 23 are mounted upon a rotatable axis 28 at rightangles to each other within coils 15 and 17 which are in the same plane.A rotation of the aXis'28 by means of the handle 29 changes the positionof coils 22 and 23V with respect to coils 15 and 17. When coil 22 isparallel to coil 15 the coupling between the two is maximum. Undertheseconditions coil 23 is at right angles to coil 17 and the couplingbetween the two 1 is substantially zero. If the coils 22 and 23 are thenturned the coupling between 15 and 22 will be weakened and the couplingbetween coils 17 and 23 will be strengthened until coil 22 reaches aposition at a right angle to coil 17 If the coils are turned farther inthe same direction the action will be reversed and the direction ofcoupling will also be reversed from that which was present during thefirst 90 of the movement.

A similar arrangement is provided for cou- 100 pling transformers 2O and21.

The currents set up in the receiving circuit are impressed in the mannerindicated upon the grid circuit of a detector 30 of the pliotron type.In case the Signals to be 105 received are continuous wave signals thereceiving pliotron may be made to produce the local oscillationsnecessary for heterodyne operation by means of a loose coupling betweenthe coil 31 in the plate circuit and. 110

the coil 32 in the grid circuit.

The receiving system which I have de scribed is adapted to receivesignals from either station A or station B without interference whenwaves of the same wave length 115 antennae extend in a direct linebetween sta- 120 tions A and B and that their centers of distribution 4and 5 are just a quarter of a wave length apart. An impulse travelingfrom A will reach antenna 1 a quarter of a period before it reachesantenna 2 and hence 125 the current produced thereby in antenna 1 willlead the current produced in antenna 2 by 90. These two currents may berepresented on the diagram of Fig. 3 by the vectors Al and Ag'. Animpulse traveling from' 13o VA1 and A2 are in phase.

1 B will, on the other hand, reach antenna 2 'the current in theinductivebranch lags 45 behind the main current, the` vectors of thesecurrents may be indicated by Af, All, Bf, and B1. Assume the sameconditions for the circuit connected tov antenna 2 and the currents inthe two branches may be represented by vectors A02, AZ, Bc2 and Blz. If

'nowthe coupling transformers are so adjusted that the inductive branchonly of` the first circuit is coupled to the receiving circuit and thecapacitative branch only of the second circuit is coupled to thereceiving circuit the currents impressed upon the receiving circuit willbe represented by the vectors Al, Bil, Ag' and BCZ.- It will be seenfrom the diagram that vectors B1,L and Bc2 are directly opposite inphase and vectors Therefore if B1 and B2 are equal in intensity the willneutralize eachother while A1 and c2 will act cumulatively in thereceiving circuit. The two currents Bi1 and B2, may easily be adjustedto the same intensity by varying the coupling of one or both of theintensity coupling transformers 9 and 10.

In case 'it iis desired to receive lsignals from station' B the effectof signals from station A may easily be neutralized by coupling thecapacitative branch only of the first antenna circuit to the receivingcircuit and coupling the inductive branch only of the second circuit tothe receiving circuit.

While in the above explanation the pre ferred` conditions of operationare set forth it is by no means essential to the successful operation ofmy receiving system that the phase relations of the diiferent currentsshould correspond with those illustrated in Fig. 3. It is apparent thatby suitable design of the phase shifting circuit currents may beproduced in the two branches which lead or follow the main current bymore than 45 and that by varying thelcoupling between the circuitcurrents may be impressed upon the receiving circuit which lead orfollow the currents produced in the antennae by any desired angle. Henceit will always be possible to so adjust the apparatus that the currentsproduced by the undesired signals in the two antennae will beneutralized in theV receiving circuit. While under other conditionsthan-those described it may not bepossible to `make the adjustment sothat the two currents produced by the desired signals will be directlyin phase, they will always combine with each other at some angle lessthan 180 and will not neutralize each other when the apparatus isadjusted to neutralize the undesired signals as long as the phaserelation between the two currents from station A are not the same as thephase relation between the two currents from station B.

The receiving system which I have described is also adapted for use in asystem for preventing the reception of signals by unauthorized persons.In case it is desired to receive signals from station A and prevent thereception of the signals at some other' point an interfering wave of thesame length as the signaling wave may be produced at station B.I Thiswave may be 'neutralized at points between A and B because of the factthat at such points the two waves will be traveling in oppositedirections, and hence the phase relation between the two currents fromstation A will be different from the phase relation between the twocurrents from station B. At other points, however, in line with stationsA and B where the two waves travel in the same direction the interferingwave cannot be neutralized and hence the signals fro station A cannot bereceived. While it might be possible in case stations A and B areseparated by a great distance to receive the signals from A at pointsnearer station A than station B, by reason of the different intensitiesof the Wave, at points nearer station B than station A the interferingwave would naturally be much stronger than the signaling wave and hencesignals could not be received when the two waves were traveling in thesame direction.

In case it is desired to prevent the reception of signals at a singlepoint and this point does not happen to be in line with the transmittingand receiving stations, the interfering wave may be produced at a pointbetween the transmitting station and the point at which it is desired toprevent reception, the only requirement being that this point shall beso chosen that the interfering wave may be neutralized at the receivingstation. In case it is desired to prevent 1eception at a large number ofpoints scattered over a single area it may be necessary to produce twoor more sets of interfering waves. One manner in which this may beaccomplished is indicated in Fig. 4 which represents one form ofreceiving diagram which may be obtained with a receivingcircuit such asI have described. In this case the receiving apparatus is so adjusted asto neutralize interfering waves produced at the two stations C and D andreceive at the same time signals from station A. At any point fartheraway from' station A than stations C and D it would not be possible toneutralize both interfering waves and at the same time receive signalsfrom station A with the maximum intensity. It might, however, bepossible to neutralize the iiiterfering Waves from C and D at some pointas E in the line with the receiving and transmitting stations, but inthis case the intensity of the signals from A would be represented bythe small vector O F on the receiving diagram. To prevent-even thepossibility of receivin signals at such a point as E three inter eringwaves ma be produced at points such as G, H and as indicated in Fig. 5.All of these waves may be neutralized at the receiving staton byarranging the receiving-circuit so that it will give-a receiving diagramsuch as that shown in Fig. 5. If the stations are properly located inthis manner it would be absolutely impossible to neutralize all of theinterfering waves at a point farther removed from the transmittingstation A than the interfering stations G, H and I.

In case it is desired to receive signals from a station K, as indicatedin Fig. 4, and the elfective direction of the receiving antenna is inthe direction of K, C, it will not be possible to neutralize at the sametime interfering waves from stations C and D. If, however, the antennacould be so adjusted that its effective direction would be in thedirection A, E, it is apparent that the signals from K might be receivedand at the same time the interfering waves from C and D neutralized. Onemanner in which this desirable result may be brought about is indicatedin Fig. 6. In this case two similar receiving antennae 33 and 34 areprovide-d extending in opposite directions from the receiving stationand two other similar antennae 35 and 36 extend from the receivingstation in directions at right angles to the direction of antennae 33and 34. The eX- treme ends of antennae 35 and 36 are grounded and thestation ends are connected through an impedance which may be of anydesired form, but which in the present case I have indicated as a seriesof condensers 37. By connecting antennae 33 and 34 to different pointsalong the impedance 37 the effective direction of the antenna systemmaybe varied. For example, if both antennae 33 and 34 were connected tothe central point of the impedance37, which is a neutral point withrespect to antennae 35 and 36, the effective direction of the systemwill be along the line of the antennae 33 and 34. If, however, theconnections are made at 4some other points as indicated the effectiveis, if antenna 34 were connected to antenna 36 and antenna 33 wereconnected to antenna 35, the effective direction of the system would healong a line intersectiig the angle between antennae l34 and 36. avingadjusted the antenna system so that its effective direction is thatdesired the reception of signals and the neutralization of interferenceis accomplished in the same manner as with the antenna system shown inFig. l, the phase shifting means in this case being indicated at 38 and39 in simplilied for The form of diagram indicated in Fig. 5 could notbe obtained with an antenna system such as that shown in Figs. 1 and 6because of the fact that in this case it is necessary to eliect thecomplete neutralization of signals from three different directions. Inorder to accomplish this result a double system such as that indicatedin F ig. 7 may be employed. In this case four antennae are used. Two ofthese 40 and 41 are of the long horizontal type while the other two, 42and 43, may be of the umbrella type, or any other desired form havingtheir centers of distribution located close to the receiving station. Inreceiving signals with this system for neutralizing the interferencefrom stations Gr, H. and I the adjustment may be made as follows: Thephase shifting devices 44 and 45 may both be adjusted so as toneutralize the interference from G and H. Phase shifting devices 46 and47 may then be adjusted to neutralize the interference from station I.As a result the effect of waves coming from al1 three directions G, Hand I will be eliminated in the receiving circuit 48, and signals bereceived from A with maximum intensity..

The receiving system which I have described is also of great utility inneutralizing the eiect of strays. When the system is adjusted toneutralize interfering waves coming from any direction the effect ofstrays coming from that direction will also beneutralized.

I -nd it preferable in carrying out my 1nvention that the receivingantennae should be aperiodic and that the intermediate c1rcuits whichcontain the phase shiftmg device should also be aperiodic. By arrangingthe apparatus in this way so that the phase differences are obtained 1nuntuned circuits the adjustment of the apparatus is rendered much morenearly independent of frequency variations than would be the case iftuned circuits were employed before the currents are impressed upon thereceiving circuit and the neutralization of strays is also rendered muchmore effective.

v What I claim as new .and desire to secure by Letters Patent of theUnited States, is

1. The combination in a radio receiving system of a receiving station,two fixed horizontal receiving antennae extending in opposite directionsfrom said receiving station, said antennae serving as the sole means forcollecting energy from the ether, a receiving circuit associated withsaid antenn and means at the receiving station for shifting the phase ofcurrents impressed from said antennae upon said receiving circuit sothat the currents produced by the desired signals will add in saidreceiving circuit and currents produced by waves of the same wave lengthas the signaling wave coming from other directions will be neutralizedin said receiving circuit.

2. The combination in a radio receiving system of two fixed horizontalreceiving antenn extending in opposite directions from a receivingstation, each of said antennee having a length of at least the order ofmagnitude of a quarter of the wave length of the signals which are to bereceived, said antennae serving as the sole means for collecting energyfrom the ether, a receiving circuit associated with said antennae andmeans at the receiving station for shifting the phase of currentsimpressed from said antennae upon said receiving circuit so that thecurrents produced by the desired signals will add in said receivingcircuit and currents produced by waves of the same wave length as thesignaling wave coming from other directions will be neutralized in saidreceiving circuit.

3. The method of radio signaling which permits a desired reception andprevents an undesired reception of radio signals which consists inproducing a signaling wave and in producing an interfering wave of thesame wave length as the signaling wave and which travels in a differentdirection from the signaling wave at points where it is de-. sired toreceive the signals and in the same general direction as the signalingwave at points where it is desiredto prevent the reception of thesignals and receiving signals at a point where the two waves aretravelling in different directions.

4. The method of radio signaling which consists in producing a signalingwave, producing an interfering wave of the same wave length asthexsignaling wave and which travels in a different direction from thatof the signaling wave at certain points where it is desired to receivethe signals and inthe same general direction as the signaling wave atother points and receiving signals atl points where the two waves aretraveling in diierent directions by neutralizing the effect in thereceiving apparatus of the interferingl wave.' l

- 5. The method of radio signaling which` consists in transmittingsignals by means of a signaling wave, producing a plurality ofinterfering waves of the same wave lengt as the signaling wave and whichtravel inl different directions from that of the signaling wave atcertain points where it isdesired to receive the signals and in the samegeneral direction as the signaling wave at other points and receivingthe signals at a point where the interfering waves travel in a dii'erentdirection from that of the signaling wave by neutralizing the effects ofthe interfering waves in the receiving apparatus.

6. The combination in a radio receiving system of an aperiodic receivingantenna, a receiving circuit'associated therewith and means for varyingthe phase of the current impressed upon the receiving circuit from thereceiving antenna, said phase varying means comprising an aperiodicintermediate circuit having two portions with different phase anglecharacteristics, means for cou-d p ling both of said portions to thereceiving circuit, and means for simultaneously varying .the coupling ofboth portions to the receiving circuit.

7. The combination in a radio receiving system of an aperiodic receivingantenna, a receiving circuit associated therewith and ineans for varyingthe phase of the current impressed upon the receiving circuit from thereceiving antenna, said phase varying means comprising an aperiodicintermediate circuit having two arallel branches having different phaseang e characteristics, means for coupling both of said branches to thereceiving circuit, and means for simultaneously varying the coupling ofboth branches to t e receiving circuit.

8. The combination in a radio receiving system of an aperiodic receivingantenna, a receiving circuit associated therewith and means for varyingthe phase of the -current impressed upon the receiving circuit from thereceiving antenna, said phase varying means comprising an aperiodicintermediate circuit having two parallel branches having different phaseangle characteristics, means for coupling both of said branches to thereceiving circuit, and means for simultane-l ously varying the couplingof both branches to the receiving circuit, said coupling means being soarranged that when the coupling of one branch is at a maximum thecoupling of the other branch is a minimum.

9. The combination in a radio receiving system of an aperiodic receivingantenna, a resonant receiving circuit associated therewith, and meansfor varying the phase of the current impressed upon the receivingcircuit from the receiving antenna, said phase varying means com risingan aperiodic, intermediate circuit aving twoportions of dii'erent phaseangle characteristics, means for coupling both of said portions to thereceiving circuit, and means for simultaneously varying the .coupling ofboth portions to the receiving circuit, said 'coupling means being soarranged that as the coupling of'one portion is increased the couplingof the other portion is decreased.

10. The combination in a radio receiving system of two fixed aperiodicreceiving antennae, a resonant receiving circuit associated with saidantennae, and means forv varying the phase of the current impressed uponthe receiving circuit from the two antennae comprising an aperiodicintermediate circuit between each antennae and the receiving circuit,each of said intermediate circuits comprising two portions havingdifferent phase angle characteristics, means for coupling both of saidportions of each intermediate circuit to the receiving circuit, andmeans for simultaneously varying the coupling of both portions of eachintermediate circuit to the receiving circuit.

11. The combination in a radio receiving circuit of two fixed aperiodicreceiving antennae, a resonant receiving circuit associated with saidantennae, and means for varying the phase of the current impressed uponthe receiving circuit from the two antennae comprising an aperiodicintermediate circuit between each antenna and the receiving circuit,each of said intermediate circuits comprS'ing two parallel brancheshaving different phase angle characteristics, means for coupling both ofsaid branches of each intermediate circuit to the receiving circuit, andmeans for simultaneously varying the coupling of both branches .of eachintermediate circuit to the receiving circuit.

12. The combination in a radio receiving system of two fixed aperiodicreceiving antennae extending in opposite directions from a receivingustation, a receiving circuit associated with said antennae and means forvarying the phase of the current impressed upon the receiving circuitfrom the two antennae comprising an aperiodic intermediate circuitbetween each antenna and the receiving circuit, each of saidintermediate circuits comprising two parallel branches one of which hasa resultant capacitative impedance and the other a resultant inductiveimpedance, means for coupling both of said branches of each intermediatecircuit to the receiving circuit, and means for simultaneously varyingthe coupling of both branches of each intermediate circuit to thereceiving circuit, said coupling means being so arranged that as thecoupling of one branch is increased the coupling of the other branch isdecreased.

13. The combination in a radio receiving system of a receiving antenna,a receiving circuit associated therewith and means for varying the phaseof the current impressed upon the receiving circuit from the receivingantenna, said phase varying means comprising an intermediate circuithaving two parallel branches one of which has a resultant capacitativeimpedance and the other ing antenna, said phase varying means comiprising an intermediate circuit having two parallel branches one ofwhich. has a resultant capacitative impedance and the other a resultantinductive impedance, means for coupling both of said branches to thereceiving circuit, and means for simultaneously varying the coupling ofboth branches to the receiving circuit, said coupling means being soarranged that ywhen the coupling of one branch is a maximum the couplingof the other branch is a minimum. y

15. The combination in a radio receiving system of a receiving antenna,a receiving circuit associated therewith and means for varying the phaseof the current impressed upon the receiving circuit from the receivingantenna, said phase varying means comprisingan intermediate circuithaving two parallel branches one of which has a resultant capacitativeimpedance and the other a resultant inductive impedance, means forcoupling both'of said branches to the receiving circuit, and means forsimultaneously varying the coupling of both branches to the receivingcircuit, said coupling means being so arranged that as the coupling ofone branch is increased the coupling of the other branch is decreased.

16. The combination in a radio receiving system of two fixed receivingantennae eX- tending in opposite directions from a receiving station, areceiving circuit associated with said antennae and means for varyingthe phase of the currents impressed upon the receiving circuit from thetwo antennae comprising an intermediate circuit between each antenna andthe receiving circuit, each of said intermediate circuits comprising twoparallel branches one of which has a resultant capacitative impedanceand the other a resultant inductive impedance, means for coupling bothof said branches of each in' termediate circuit to the receivingcircuit, and means for simultaneously varying the coupling of bothbranches of each intermediate circuit to the receiving circuit.

17. The combination in a radio receiving system of a receiving station,two fixed horizontal receivingantennae extending in different directionsfrom said receiving station, said antennae serving as the sole means forcollecting energy from the ether, a' receiving circuit associated withsaid antennae and means at the receiving station for shifting the phaseof currents impressed 4from said antennae upon said receiving circuit sothat the currents produced by the desired signals will add in saidreceiving circuit' antennae having their centers of distributionseparated by a distance of at least the order of magnitude of a quarterwave length of the signals to be received, at least one of said antennaebeing of the horizontal type extending away from the receiving stationand serving as the sole means for collecting energy from the ether andconveying it to the receiving station from the direction in which itextends,.,a receiving circuit associated with said antennae and means atthe receiving station for shifting thephase of currents impressed fromsaid antennae upon said receiving circuit so that the currents producedby the desired signals will add in said receiving circuit and currentsproduced by waves of the same, wave length as thesignaling waves comingfrom other directions will be neutralized in said receiving circuit.

19. The combination in a radio receiving system of a receiving circuit,two receiving antennae, one of which has its center of distributionlocated near the receiving station and the other of which is of thehorizontal type extending away from the receiving station and having itscenter of distribution located at a point separated from the receivingstation by a distance of at least the order of magnitude of a quarterwave length of the signals to be received, a receiving circuitassociated with said antennae and means for shifting the phase ofcurrents impressed from said antennae upon said receiving circuit sothat the currents produced by the desired signals will add in saidreceiving'circuit and currents produced by waves of the same wave lengthas the signaling wave coming from other directions will be neutralizedin said receiving circuit.

20. The combination in a radio receiving system of two fixed receivingantennae, a resonant receiving circuit associated with said antennae,means for simultaneously impressing upon said receiving circuit fromeach of said antennae currents derived from the same signal wave butdiffering in phase, comprising two portions of the receiving systemhaving different phase angle characteristics, means for coupling both ofsaid portions to the receiving circuit and means for simultaneouslyvarying the coupling of both portions to the receiving circuit.

21. The combination in a radio receiving system of a receiving station,a plurality of receiving antennae at least two of which have theircenters of distribution separated by a distance of at least the order ofmagnitude of a quarter wave length of the signals to he received, areceiving circuit associated with said antennae, means associated withone pair of said antennae for neutralizing in the receiving circuit theeffect of signaling waves coming from a certain predetermined direction,and means associated with another pair of said antennae for neutralizingat the same time in the receiving circuit the effect of signaling wavescoming from another direction.

22. The method of adjusting a radio receiving system comprising aplurality of fixed receiving antennae to receive radio signals of agiven wave length coming from a desired direction to the exclusion ofsignals of the same wave length coming from other directions whichconsists 'in first neutralizing the effect in a receiving circuit ofsignals coming from one of the l'other directions by adjusting thecoupling between one pair of antennae and the receiving circuit and thenneutralizing the effect in the receiving circuit of signals coming fromanother of the undersired directions by adjusting the coupling betweenanother pair of antennae and the receiving circuit.

23. Phase varying means comprising a pair of coupling transformers eachof which consists of a fixed coil and a. coil movably mounted forrotation with respect to the fixed coil, the movable coils of the twotransformers being arranged so that they may be rotated. simultaneouslywith respect to the fixed coils and that when the couplin of onetransformer is a maximum the couing of the other is a minimum.

24. Phase varying means comprising a pair of coupling devices adapted toimpress two currents of different phase angle charl acteristics upon anelectric circuit and means for simultaneously varying the coupling ofthe two devices. f

25. Phase varying means comprising a Ipair of coupling devices adaptedtoimpress two currents of different phase angle characteristics upon anelectric circuit and means for simultaneously varying the coupling ofthe two devices in such a way that when the coupling of one device is amaximum the coupling of the other device is a minimum.

In witness whereof, I have hereunto set my hand this 13th day ofSeptember, 1918.

ERNST F. ALEXANDERSON.

